1. Field of the Invention
This invention relates to a metal halide lamp which can be used as a light source in various apparatuses such as liquid-crystal projectors and lighting equipments.
2. Description of the Related Art
Liquid-crystal projectors enlarge images of characters and figures, and project and display the enlarged images. In general, light sources in the liquid-crystal projectors are required to output light at given power levels. Since metal halide lamps have high luminous efficiencies and excellent color rendering performances, they are frequently used as light sources in the liquid-crystal projectors.
Japanese published unexamined patent application 3-219546 discloses a metal halide lamp having an arc tube filled with metal halide. In the lamp of Japanese application 3-219546, the metal halide uses iodide or bromide containing neodymium, dysprosium, or cesium.
In general, metal halide lamps are operated by rectangular electric waves having low frequencies equal to about 200 Hz. It is known to operate metal halide lamps by electric power having high frequencies. In this case, operation circuits for the metal halide lamps can be miniaturized.
When a metal halide lamp is operated by high-frequency electric power, an arc therein and a light emitting region around the arc tend to waver. Thus, in this case, resultant light outputted from the metal halide lamp tends to flicker.
Even when a metal halide lamp is operated by low-frequency rectangular electric wave, an arc therein sometimes flickers.